Waterborne acrylic coatings can deliver performance comparable to traditional solvent-borne coatings while meeting increasingly stringent coating VOC emission regulations. It is known in the coatings art that the formation of a latex film can be facilitated by incorporating a coalescing agent in the latex emulsion. These coalescing agents, or coalescents, facilitate the individual latex particles coming together to thereby form a continuous film at a given temperature by reducing the minimum film-forming temperature (MFFT) of the latex polymer. Thus, as used throughout, the coalescents of the invention reduce the minimum film-forming temperatures of the coating compositions in which they are used, as further described below.
Acetoacetoxyethyl methacrylate (AAEM) is a functional monomer used to make self-crosslinking, room-temperature-cure emulsion copolymers that may be used to produce coatings having good hardness and chemical and block resistance. Once incorporated into the copolymer, the acetoacetoxy-functionality of the AAEM monomer can cross-link via an “oxidative cure” or react with an added cross-linker such as a diamine to produce a cured film.
One of the recognized drawbacks of the acetoacetoxy moiety of AAEM is that it is known to be hydrolytically labile and a decline in film performance of copolymers prepared from this monomer has been correlated with the heat history and age of the copolymers. To avoid this degradation in performance, manufacturers have added volatile amines to convert the acetoacetate to its enamine tautomer and limit the hydrolysis. While this slows the hydrolysis, it does not completely eliminate it. Also, the addition of a volatile amine component can introduce a disagreeable odor to the coating product during application.
U.S. Pat. No. 4,215,195 to Ponticello et al. discloses compounds, including methacrylamides and acetoacetamidoethyl methacrylate, that can be homopolymerized or copolymerized with each other or with polymerizable ethylenically unsaturated monomers to give crosslinkable polymers. Polymers made from monomers having amide functionality are said to exhibit improved hydrolytic stability.
U.S. Pat. Nos. 4,855,349 and 5,073,445 to Ingle disclose permanently flexible and non-tacky coating mastic and caulking compositions that contain one or more polymers having a Tg of about −50° C. to about −10° C. and pendant functional groups attached to the polymer backbone having the formula —R1—C═O—CH2—X, in which R1 is a divalent organic radical at least 3 atoms in length, and X is organoacyl or cyano. Acetoacetoxy-ethyl methacrylate is exemplified.
U.S. Pat. No. 5,296,530 to Bors et al. discloses a method for light-assisted curing of coatings by providing coatings with an enamine content sufficient to enhance the cure rate of the coatings. According to the disclosure, a quick-curing coating is prepared from a polymer having acetoacetyl groups, in which substantially all of the acetoacetyl groups have been converted to enamine functionality, for example by treatment with ammonia or primary amine. Coatings which are so prepared are said to cure more quickly under sunlight or ultraviolet light than coatings which contain the acetoacetyl functional polymer which has not been converted to enamine. Acetoacetoxy-ethyl methacrylate is exemplified.
U.S. Pat. No. 5,494,975 to Lavoie et al. discloses the preparation of polymers containing functional acetoacetate groups and then, following the polymerization, reacting the acetoacetate group with a functional amine to form an enamine. A preferred monomer is acetoacetoxyethyl methacrylate. Examples of other monomers said to be useful for introduction of acetoacetate functionality include acetoacetoxyethyl acrylate, acetoacetoxypropyl methacrylate, allyl acetoacetate, acetoacetoxybutyl methacrylate, and 2,3-di(acetoacetoxy)propyl methacrylate.
U.S. Pat. No. 5,484,849 to Bors et al. discloses air curing polymer compositions which contain an acetoacetate-functional polymer and an autoxidizable material. The compositions cure on exposure to oxygen. The acetoacetate-functional polymers can be prepared by means known in the art. A preferred method is polymerization through incorporation which includes an acetoacetate-functional monomer, with acetoacetoxy-ethyl methacrylate, acetoacetoxypropyl methacrylate, and allyl acetoacetate being exemplified. Examples of other monomers said to be useful include acetoacetoxyethyl acrylate, acetoacetoxybutyl methacrylate, and 2,3-di(acetoacetoxy)propyl methacrylate.
J. Stewart Witzeman et al. reported that acetoacetylated polymers and resins have been shown to be capable of undergoing a variety of crosslinking reactions, and that the best industrial method for acetoacetylation of monomeric and polymeric materials is by transesterification with t-butyl acetoacetate. They also reported that among the processes which have been used to effect crosslinking of acetoacetylated polymeric materials are reactions with diamines, melamine, aldehydes, isocyanates, chelation with metals, and Michael reaction with activated olefins. They further reported that acetoacetylated materials can be prepared by treating a nucleophile with diketene, from the thermal reaction of 2,2,6-trimethyl-4H-1,3,-dioxin-4-one, TKD, the diketene-acetone adduct, or by transesterification with another acetoacetate. See Comparison of Methods for the Preparation of Acetoacetylated Coating Resins, Witzeman, J. S.; Dell Nottingham, W.; Del Rector, F. J. Coatings Technology; Vol. 62, 1990, 10 1.
U.S. Pat. No. 5,756,826 to Hanselmann discloses a process for preparing acetoacetates, in which (2-acetoacetamido-2-methylpropyl)methacrylate may be formed by reacting 2-amino-2-methyl-1-propanol with diketene, the adduct then being reacted with thiodiphenylamine and methacrylic anhydride, followed by further thiodiphenylamine to form the (2-acetoacetamido-2-methylpropyl)methacrylate. Alternatively, the reaction may be carried out in a similar method, but using different alcohols.
U.S. Pat. No. 5,872,297 to Trumbo discloses ethylenically-unsaturated 1,3-diketoamide functional compounds, polymers comprised thereof, and latex formulations containing polymeric ingredients having 1,3-diketoamide functional pendant moieties. The 1,3-diketoamide functional pendant moieties are said to have excellent hydrolytic stability.
U.S. Pat. Nos. 5,945,489 and 6,025,410 to Moy et al. disclose liquid oligomeric compositions made by the Michael addition reaction of acetoacetate functional donor compounds with multifunctional acrylate receptor compounds where the equivalent ratios of multifunctional acrylate to acetoacetate vary from greater than or equal to 1:1 to greater than or equal to 13.2:1, depending on the functionality of both multifunctional acrylate and acetoacetate. The use of multifunctional (diacrylates, triacrylates, and tetraacrylates) acrylates results in residual unsaturation in the oligomers that is useful for subsequent cross-linking. The liquid oligomers may thus be further crosslinked to make coatings, laminates and adhesives.
U.S. Pat. No. 5,990,224 to Raynolds et al. discloses low foam waterborne polymer compositions stabilized against gelling due to the addition of a poly(alkylenimine) by addition of surfactants. Enamine-functional polymers are said to represent a preferred embodiment of polymers, and may be prepared by reacting a polymer having acetoacetoxy groups with ammonia or a primary or secondary amine, such as polyethylenimine (PEI). Acetoacetoxy-type functional polymers are said to be useful, and may be prepared by free radical emulsion polymerization of vinyl monomers having an acetoacetoxy functionality with other vinyl monomers. Preferred monomers of this type are said to include acetoacetoxy-ethyl methacrylate, acetoacetoxyethyl acrylate, acetoacetoxy(methyl)ethyl acrylate, acetoacetoxypropyl acrylate, allyl acetoacetate, acetoacetamido-ethyl(meth)acrylate, and acetoacetoxybutyl acrylate, with acetoacetoxyethyl methacrylate (AAEM) representing a particularly preferred such monomer. Acetoacetoxyethyl methacrylate is the monomer used in the examples.
U.S. Pat. No. 5,962,556 to Taylor discloses the use of a monomer represented by formula:R1—CH═C(R2)C(═O)—X1—X2—X3—C(═O)—CH2—C(═O)—R3 where R1 is a hydrogen or halogen; R2 is a hydrogen, halogen, C1-C6 alkylthio group, or C1-C6 alkyl group; R3 is a C1-C6 alkyl group; X1 and X3 are independently O, S or a group of the formula: —N(R1)—, where R1 is a C1-C6 alkyl group; X2 is a C2-C12 alkylene group or C3-C12 cycloalkylene group. The alkyl and alkylene group described may be straight or branched. Preferred monomers are said to include acetoacetoxyethyl (meth)acrylate, acetoacetoxy(methyl)ethyl (meth)acrylate, acetoacetoxypropyl(meth)acrylate and acetoacetoxybutyl (meth)acrylate, with the term “(meth)acrylate” used in the patent to denote methacrylate or acrylate. The only such monomer exemplified is acetoacetoxyethyl methacrylate. U.S. Pat. No. 6,262,169 to Helmer et al., and U.S. Pat. Publn. No. 2003/0134973A1 to Chen et al., likewise disclose polymers having acetoacetoxy functional groups.
GB 2 335 424A, related to curable compounds and polymers having reactive functional groups, discloses an unsaturated compound (A), that can be 2-aceto-acetoxyethyl methacrylate, 3-acetoacetoxypropyl methacrylate, allyl acetoacetate, or an acetoacetate of a polyol such as trimethylol propane or pentaerythritol, reacted with a compound (B) which can be inter alia an acrylate for example having epoxide functionality, an acrylamide, or a maleate diester, to obtain a compound that can, itself, be used as a monomer, or further reacted with another compound having an activated double bond. For example, according to the disclosure, acetoacetoxyethyl methacrylate is reacted with glycidyl acrylate to produce bis(carboglycidoxyethyl)acetoacetoxyethyl methacrylate, and dimethyl malonate is reacted with neopentyl glycol to produce a neopentyl malonate polyester. A further disclosure is trimethylolpropane reacted with t-butyl acetoacetate to form 1,1,1-tris(acetoacetoxymethyl)propane.
U.S. Pat. Publn. No. 2008/0194722 discloses a hardenable dental composition that includes a polymerizable compound having at least one cyclic allylic sulfide moiety and at least one (meth)acryloyl moiety. The polymerizable compound is referred to as a hybrid monomer or a hybrid compound, and can be a substituted acetoacetoxyethyl methacrylate. See Formula 1a-5. The hardenable component is one that is capable of polymerization and/or crosslinking reactions including, for example, photopolymerization reactions and chemical polymerization techniques (e.g., ionic reactions or chemical reactions forming radicals effective to polymerize ethylenically unsaturated compounds, (meth)acrylate compounds, etc.) involving one or more compounds capable of hardening. Hardening reactions are also said to include acid-base setting reactions such as those common for cement forming compositions (e.g., zinc polycarboxylate cements, glass-ionomer cements, etc.).
U.S. Pat. Publn. No. 2010/0081769 discloses a process for producing a linear block copolymer, useful as a dispersant for pigment, wherein the block copolymer comprises acetoacetyl amine functional groups which serve as pigment anchoring groups. The acetoacetyl amine functional groups can be formed by reacting hydroxyl functional groups with an acetoacetate agent, and then reacting the resulting acetoacetate functional groups with a primary amine. One example of ethylenically unsaturated acetoacetate monomers that is useful for introduction of acetoacetate functional group into the block copolymer can be acetoacetoxyethyl methacrylate. Examples of other monomers that can be used to introduce an acetoacetate functional group into the block copolymer can include acetoacetoxyethyl acrylate, acetoacetoxypropyl methacrylate, acetoacetoxypropyl acrylate, allyl acetoacetate, acetoacetoxybutyl methacrylate, acetoacetoxybutyl acrylate, and the like.
Though acetoacetoxy-functional monomers are known to be useful in polymerization processes, and the polymers and copolymers made from such processes find use in coating compositions, there remains a need in the art for monomers useful in coating compositions, whether UV-curable monomer mixtures, solution acrylics, or emulsion polymers known as latexes, and that may be used to produce coatings having good hardness and chemical and block resistance, and that exhibit improved hydrolytic stability. It would be an additional advantage if such molecules might be used as coalescents, provided as mixtures with latex emulsion polymers to provide coating compositions having improved coalescing properties.